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<meta name="author" content="Jan Aerts">
<title>Data Management</title>
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<body id="_keyvalue_stores" class="article toc2 toc-left">
<div id="header">
<h1>Data Management</h1>
<div class="details">
<span id="author" class="author">Jan Aerts</span><br>
<span id="email" class="email"><a href="mailto:[email protected]">[email protected]</a></span><br>
</div>
<div id="toc" class="toc2">
<div id="toctitle">Table of Contents</div>
<p><span class="toc-root"><a href="index.html">Data Management</a></span></p><ul class="sectlevel1">
<li><a href="_relational_database_management_systems.html">1. Relational Database Management Systems</a>
</li>
<li><a href="_nosql_an_introduction.html">2. NoSQL: an introduction</a>
</li>
<li><a href="_keyvalue_stores.html"><span class="toc-current">3. Key/value stores</span></a>
<ul class="sectlevel2">
<li><a href="_keyvalue_stores.html#_implementations">3.1. Implementations</a>
</li>
</ul>
</li>
<li><a href="_document_oriented_databases.html">4. Document-oriented databases</a>
</li>
<li><a href="_graph_databases.html">5. Graph databases</a>
</li>
<li><a href="_arangodb.html">6. ArangoDB</a>
</li>
<li><a href="_arangodb_interfaces.html">7. ArangoDB interfaces</a>
</li>
</ul>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_keyvalue_stores">3. Key/value stores</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Key/value stores are a very simple type of database. The only thing they do, is link an arbitrary blob of data (the value) to a key (a string). This blob of data can be a piece of text, an image, etc. It is not possible top run queries. Key-value stores therefore basically act as dictionaries:</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="assets/gouge.png" alt="gouge"></span></p>
</div>
<div class="paragraph">
<p>A key/value store only allows 3 operations: <code>put</code>, <code>get</code> and <code>delete</code>. Again: you can <em>not</em> query.</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="assets/keyvalue-1.png" alt="keyvalue 1"></span></p>
</div>
<div class="paragraph">
<p>For example:</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="assets/keyvalue-2.png" alt="keyvalue 2"></span></p>
</div>
<div class="paragraph">
<p>This type of database is very scalable, and allows for fast retrieval of values regardless of the number of items in the database. In addition, you can store whatever you want as a value; you don’t have to specify the data type for that value.</p>
</div>
<div class="paragraph">
<p>There basically exist only 2 rules when using a key/value store:</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>Keys should be unique: you can <em>never</em> have two things with the same key.</p>
</li>
<li>
<p>Queries on values are not possible: you cannot select a key/value pair based on something that is in the value. This is different from e.g. a relational database, where you use a <code>WHERE</code> clause to constrain a result set. The value should be considered as opaque.</p>
</li>
</ol>
</div>
<div class="paragraph">
<p><span class="image"><img src="assets/keyvalue-3.png" alt="keyvalue 3"></span></p>
</div>
<div class="paragraph">
<p>Although (actually: because) they are so simple, there are very specific use cases for key/value stores, for example to store webpages: the key is the URL, the value is the HTML. If you go to a webpage that you visited before, your web browser will first check if it has stored the contents of that website locally beforehand, before doing the costly action of downloading the webpage over the internet.</p>
</div>
<div class="sect2">
<h3 id="_implementations">3.1. Implementations</h3>
<div class="paragraph">
<p>Many implementations of key/value stores exist, probably the easiest to use being Redis (<a href="http://redis.io" class="bare">http://redis.io</a>). Try it out on <a href="http://try.redis.io" class="bare">http://try.redis.io</a>. ArangoDB (www.arangodb.org) is a multi-model database which also allows to store key/values (see below).</p>
</div>
</div>
</div>
</div>
<div class="paragraph nav-footer">
<p>← Previous: <a href="_nosql_an_introduction.html">NoSQL: an introduction</a> | ↑ Up: <a href="index.html">Data Management</a> | Next: <a href="_document_oriented_databases.html">Document-oriented databases</a> →</p>
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Last updated 2023-11-13 10:40:23 +0100
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